Luis Sera

He appear in Resident Evil 4 is a twenty-eight-year-old Spaniard who befriends Leon S. Kennedy early in the game, and teams up with him to escape the village. He claims to have formerly worked as a police officer in Madrid. However, he later admits to Leon that he is actually a researcher working for Osmund Saddler.

When he becomes disillusioned with Saddler, and the work he was performing for him, Sera decided to betray Saddler and steal the sample of Las Plagas. Eventually, though, Saddler catches up with him and orders his followers to tie him up and put him a closet to be executed. However, Leon Kennedy finds Sera in the cabin, and frees him. Sera later helps Leon and Ashley Graham fight off a mob of Ganados. He then goes to get the sample and vaccine for the Plagas parasite for Leon and Ashley.

Unfortunately, Saddler impales Sera through the chest with his tentacle tail. Before dying, Sera gives Leon some pills to suppress the growth of the Plaga in his body, as well as leaving behind all of his research notes - scattered throughout the castle and island complex. These memos provide Leon with useful information on the behaviour of Las Plagas and how to destroy many of the creatures introduced during the course of the game. The plaga-removing machine which Leon and Ashley use near the end of the game was invented by Luis. It is also mentioned in one found note that he was able to remove the Plaga egg before it hatched in his body.

The "Separate Ways" scenario and "Ada's Report" documentary added to the PS2, PC and Wii version of the game expands on Luis's role in the game, depicting him as in league with Ada Wong and the organization she works for (a connection that was only implied in the main game).

When Leon is with Sera in the cabin fighting off villagers, if the player shoots him enough times (3-5 times approx.), a cutscene will start and he will kill Leon (shooting him twice in the chest), saying "Adios, Leon" before doing the deed.